The present invention relates to a method for operating a drive device which has an internal combustion engine and an exhaust gas purification device for exhaust gas of the internal combustion engine
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
The drive device of a motor vehicle serves for example for providing a torque for driving the motor vehicle. The drive device includes an internal combustion engine, in particular for providing the torque. During operation of the drive device or the internal combustion engine, exhaust gas is generated which is discharged in the direction of an external environment of the drive device.
For this reason an exhaust gas purification device is provided, which serves for purifying the exhaust gas of the internal combustion engine before it reaches the environment. The exhaust gas purification device is for example constructed as a catalytic converter. The exhaust gas purification device has an oxygen accumulator, which can generally be constructed in any desired manner. Particularly preferably the oxygen accumulator is applied to a catalytically active surface of the catalytic converter. The exhaust gas purification device having the oxygen accumulator and being configured as catalytic converter can insofar be referred to as storage catalytic converter.
The exhaust gas purification device is usually configured so that it can only convert pollutants, for example hydrocarbons, nitrogen oxide, nitrogen dioxide and carbon monoxide, when the internal combustion engine is operated stoichiometrically. During operation the drive device, however, the drive device may sometimes be operated in the so-called trailing throttle mode, i.e., the internal combustion engine is operated without introducing fuel. This leads to a large amount of uncombusted oxygen entering the exhaust gas purification device.
The exhaust gas purification device takes up or temporarily stores the thusly generated oxygen. Of course the oxygen accumulator of the exhaust gas purification device can also be loaded with oxygen in a different way, for example during a super-stoichiometric operation of the internal combustion engine. However, the greater an oxygen fill level of the exhaust gas purification device is, i.e., the more the latter is loaded with oxygen, the lower is the conversion efficiency for certain pollutants, for example nitrogen dioxide. In particular the conversion efficiency decreases to zero as soon as the oxygen fill level of the exhaust gas purification device exceeds a defined maximal oxygen fill level.
For this reason the oxygen removal operation is performed in particular when the oxygen fill level exceeds (reaches) a defined oxygen threshold fill level, which for example corresponds to the maximal oxygen fill level. During the oxygen removal operation the oxygen is removed from the exhaust gas purification device or the oxygen accumulator. For example the oxygen removal operation is performed until a defined oxygen setpoint fill level is reached. The oxygen setpoint fill level can for example correspond to an oxygen minimal fill level or an oxygen fill level that lies midway between the oxygen minimal fill level and the oxygen maximal fill level.
It would be desirable and advantageous to provide a more reliable and efficient method for operating a drive device, in an oxygen removal operation.